Screening and Characterisation of Yeast Species for Citric Acid Production Using Glycerol and Agro-waste

The present study was aimed to isolate and screen yeast species for the production of citric acid using glycerol and agro-waste. Fruit samples (orange, lime, lemon and pineapple) were collected from Bodija market in Ibadan. The samples were subjected to microbiological and physicochemical analyses. A total of 43 yeast isolates were recovered from the fruit and 17 isolates had the potential to produce citric acid after screening. Yeast isolates were identified as: Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2. The best incubation period for citric acid production by Candida tropicalis PiB10 was 120 hours (18.02 g/l), highest citric acid production (33.53 g/l) at pH 5.0, maximum citric acid production (20.84 g/l) was at 30°C, Glucose was the best carbon source, yielding 18.00 g/l of citric acid. Yeast extract was the best nitrogen source with citric acid production of 19.20 g/l and the highest production of 19.58 g/l at 200 rpm from glycerol. Meyerozyma guilliermondii LeB1 showed the highest citric acid production at 120 hours of incubation, yielding 17.02 g/l. The best pH was 5.5, yielding 35.90 g/l of citric acid. The best temperature was 30°C, with a production of 15.80 g/l, Glucose was also the preferred carbon source for this isolate, with a production of 20.13 g/l. Yeast extract was the best nitrogen source for Pichia guilliermondii LeB1, yielding 18.85 g/l. At 200 rpm from glycerol, the highest production was 22.37 g/l. This study demonstrated that Candida tropicalis, Meyerozyma guilliermondii and Candida tropicalis2 yielded high amount of citric acid using glycerol and agro-industrial wastes as substrates.